1. Field of the Invention
The invention relates to a torsional vibration damper for a motor vehicle with a drive-side transmission element and an output-side transmission element that are connected via at least two different coupling devices such that momentum flow during vibration damping is divided into first and second predetermined shares.
2. Description of the Related Art
A prior art torsional vibration damper is described in reference DE 44 44 196 A1 that has a first coupling device connected between a drive-side transmission element and an output-side transmission element. The first coupling device is a gear element that acts between the two transmission elements. This gear element, which is placed into motion during relative movements of the two transmission elements, comprises at least one planetary gearwheel of a planetary gear. According to FIG. 2 of the prior art reference, for example, a displacement movement of the drive-side transmission element is conveyed via a sun gear to the planetary gearwheel. The planetary gearwheel divides the conveyed moment into a first moment part, which is transmitted to an internal gear, and a second moment part, which reaches planetary carriers arranged on both sides of the planetary gearwheel and the internal gear. The internal gear and the planetary carriers are connected to each other via a second coupling device in the form of elastic elements running in the circumferential direction. As a result, after deformation of the elastic elements during relative movements of the internal gear and the planetary carriers, the aforementioned partial moments are recombined and conveyed to the output-side transmission element. This method, wherein a conveyed moment is first divided and then recombined is advantageous in that, thanks to the relatively low deformation of the elastic elements running in the circumferential direction, the effect achieved is approximately that of a total mass composed of a drive-side transmission element, an intermediate element and an output-side transmission element. For this reason, the apparent mass inertial moment that counteracts equidirectional fluctuations of the drive is increased, compared with a torsional vibration damper in which larger relative movements between the individual elements are possible. Moreover, low torque fluctuations are attained at the engine front. Of course, this torsional vibration damper has a fixed resonance, so that it does not act as a self-quieting system. Rather, if the torsional vibration damper remains in its resonance range for a relatively long time, damage can result.
Another prior art torsional vibration damper is described in DE 42 00 174 A1 with a drive-side transmission element and an output-side transmission element that are connected to each other via a gear having a link and a pivotable mass. The gear is part of a coupling device. The link acts on one transmission element and the mass acts on the other in articulated fashion. The link is effective as a gear element, which is placed into motion during a relative movement of the two transmission elements, whereby the speed and acceleration of the transmission elements during this relative movement, as well as the size of the movement itself, are decisive for the movement behavior of the gear element. The gear element acts as a drive for the pivotable mass. Displacements of the pivotable mass brought about by the gear element occur counter to the centrifugal force created during the rotation of the torsional vibration damper. In FIG. 1 of this reference, for example, the pivotable mass is embodied as a lever arm rotatable around a rotational point, so that when the mass is displaced from an initial state, its center of gravity is radially moved relative to the rotational center of the torsional vibration damper. As a result, because the distance of the center of gravity from the rotational center is quadratically related to the moment of inertia, the transmission element, during a change in position, must overcome a moment of inertia associated with the position and movement behavior of the pivotable mass. This offers the advantage that, when the transmission elements carry out large movements relative to each other, e.g., during passage through a resonance area or in the event of strong load alternation impacts, the apparent inertial moment of the drive-side transmission element is very high, compared with a torsional vibration damper with a mass with a movable center of gravity. Equidirectional fluctuations of the drive are therefore counteracted, resulting in low torque fluctuations at the engine front. Furthermore, because the movements of the mass continuously change the inertia of the corresponding transmission element, no unambiguous resonance point exists, so that the torsional vibration damper acts as a self-quieting system.
A problem with this torsional vibration damper is that the change in inertia brought about by the pivotable mass, in itself desirable, occurs within narrow limits.
It is an object of the invention to embody a torsional vibration damper such that, given a movable resonance frequency, the moment of inertia counteracting a load alternation impact changes sharply depending on the displacement conditions of the transmission elements.
This object is attained according to the invention by providing the vibration damper with two coupling devices wherein at least one of the coupling devices has associated with it at least one mass which moves into a different position during a relative movement of the two transmission elements. The movement of the mass changes the moment of inertia of one of the transmission elements relative to the rotational axis of the vibration damper.
By providing the torsional vibration damper with a gear device that transforms the movement of a gear element or changes the translation, the mass can be driven such that the strongest possible change in the moment of inertia is attained upon a movement of the mass. For example, the gear element may comprise a planetary gearwheel of a planetary gear in drive connection with a gearwheel of considerably larger diameter. In this case, for one rotation of the larger gearwheel, a plurality of rotations of the planetary gearwheel are needed. The advantage here is that even in the case of relatively large relative movements between the transmission elements, and a correspondingly large number of rotations of the planetary gearwheels, the large gearwheel executes only one rotation, or even only part of one rotation. Thus, when a change in rotational angle is brought about in this fashion, an eccentrically embodied gearwheel, for example, immediately undergoes a considerable change in its center of gravity relative to the rotational center of the torsional vibration damper.
In the operational mode described above, such a gearwheel moves in an oscillating fashion, so that two exactly defined end positions exist, within which the moment of inertia changes between a maximum value and a minimum value. The connection of the planetary gearwheel to the aforementioned large gearwheel may be established by an interlocking gear tooth connection. However, it is equally possible to create a friction-locking connection. It is also conceivable to drive a mass that, because of the embodiment of the gear device, moves at a higher speed than the planetary gearwheel or gear element of some other type, so that upon each relative movement of the transmission elements, very high acceleration can be applied to the mass to build up the comparatively high movement speed. The inertia counteracting such a procedure is considerable.
Instead of embodying the mass as a rotating object, the mass may also comprise radially movable elements. Due to their radial movement, the center of gravity of these elements moves radially relative to the rotational center of the torsional vibration damper. Therefore, the moment of inertia of the transmission elements is influenced. In addition, embodiments with a pair of radially movable elements are conceivable. In one such embodiment, a certain movement direction of the gear element starting from a normal position, displaces one of the pair of radially movable elements radially inward and displaces the other radially outward. Because the moment of inertia is a quadratic function of the radius of a mass from a center of rotation, the moment of inertia also changes in the event of this movement of radially movable masses. An embodiment is also conceivable in which each radially movable mass is associated with a gear element as a drive. When a plurality of such masses are used, the masses are simultaneously moved radially outward or radially inward. Understandably, the change in the moment of inertia caused by the plurality of masses is considerable. Advantageously, the change in the moment of inertia effected by the change in center of gravity of these masses relative to the rotational center of the torsional vibration damper is supported by a gear element. The gear element distributes the moment applied at one transmission element to the mass, on the one hand, and to the other transmission element or an intermediate element connected thereto, on the other. This measure allows the deformation distance of the springs running in the circumferential direction to be reduced, so that the effect created is approximately that of a total mass composed of a drive-side transmission element, an intermediate element and an output-side transmission element. Accordingly, the apparent mass moment of inertia counteracting the equidirectional fluctuations of the drive is greater than a torsional vibration damper in which larger relative movements between the individual transmission elements are possible.
Depending on the embodiment of the gear, the partial moments produced by the gear element may be independently transmitted to the output-side transmission element. This separation of the moments is known as xe2x80x9cbranching.xe2x80x9d In another design, the partial moments are recombined onto the drive-side in closed fashion. This recombination is referred to as xe2x80x9cmeshing.xe2x80x9d In the detailed description below, different examples of the invention are discussed, whereby one embodiment includes branching and the other includes meshing.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.